Smaller lavatories are helping airlines to add extra seats to new and existing aircraft for more profit, but some passengers — if they can get into the bathrooms — say they are being shortchanged.

The continuing installation of smaller and reconfigured bathrooms, which began in late 2013, has led to complaints about safety issues, say travelers and flight crew, who are concerned about restricted access for the physically disabled, as well as ease of use for other passengers.

Barry Brandes, a retired singer from Somers, New York, travels several times a year on United Airlines. At 6-foot-4, Brandes said that getting into the new lavatories on the Boeing 737-900, a single-aisle airplane, is not easy. “If I don’t duck, I hit my head on the door,” he said. “I can’t stand up completely, so I have to twist myself into a pretzel to use the facility.”

United has a total of 250 Boeing 737-800 and 737-900 aircraft that feature a combination of the new lavatory and the traditional lavatory, according to Erica Benson, a spokeswoman. In an email, she said the airplanes are reconfigured for the best use of space. In some aircraft, she noted, lavatories in first class have a new design, but have not decreased in size, while new lavatories located between first class and the first row of economy have decreased in size.

The configuration of the toilets can make it especially difficult during medical emergencies to help travelers who are incapacitated or unable to move on their own, said Jeffrey Tonjes, a spokesman for United flight attendants in the Association of Flight Attendants-CWA, a union that represents 50,000 flight attendants at 18 airlines.

“Both passenger and flight attendant are in harm’s way for injury or slowed response if we have difficulty getting to the passenger,” Tonjes said. “United Airlines is aware of this, and committed to addressing the issue about a year ago, but has been slow in getting the fix done.”

The square footage of the old and new bathrooms varies, depending on their location — whether they are in the back next to the galley, on the sides of the plane in front of the galley, mid-cabin in coach or in first class — and the model of aircraft.

This reporter recently measured the lavatories on a Boeing 757-300, which had the traditional, older bathrooms, and on a 737-800, which had the newer bathrooms.

The traditional lavatories in first class and coach on a Boeing 757-300 measured, 41 inches long by 34 1/2 inches wide by 75 inches high. On a Boeing 737-800, the new bathroom in first class measured 36 by 27 by 77, and in coach measured 39 3/4 by 24 1/2 by 77. The new lavatories, which have smaller sinks and trash receptacles, are a bit taller than the traditional bathrooms, but narrower and not as deep.

Benson, who declined to give official dimensions, said only that the newer bathrooms shrank 3 to 4 inches from the sink to the opposite wall, and lengthened 2 to 3 inches from the back of the toilet to the door.

The smaller bathrooms, combined with smaller galleys and trimmer seats with less pitch, allow space for an extra row of seats in the rear.

Doug Alder, a spokesman for Boeing Commercial Airplanes, said that airlines choose their own lavatory, galley and seat arrangements from various suppliers to create optimal use of cabin space. He declined to reveal lavatory dimensions and added, in an email, that “there is currently only one supplier for lavs across all models of the 737 — B/E Aerospace.”

Numerous phone calls requesting an interview with executives from B/E Aerospace, which has its headquarters in Wellington, Florida, were not returned.

Benson of United declined to comment on complaints about the smaller bathrooms and referred questions to Airlines for America, a trade group that represents major United States airlines. Jean Medina, a spokeswoman for the group, wrote in an email: “I’m not aware of issues or complaints on the matter.”

United is not the only airline to install smaller lavatories on its newer single-aisle aircraft. Bobbie Egan, an Alaska Airlines spokeswoman, said six of its airline’s 153 Boeing 737s have lavatories that were slightly reduced in size, and that no customer complaints have been registered. “Separately, adjusting (the seat) pitch and removing a mid-cabin lavatory and closet on these six planes enabled us to add one row of seats,” Egan wrote in an email.

Delta Air Lines flies the Boeing 737-900ER, which all have the smaller lavatories, and Airbus 320s, which are undergoing cabin modification. “A small number of the A320s now have the smaller lavs,” said Morgan Durrant, a spokesman for Delta. He said that in customer surveys, there has been no significant feedback or complaints about the size of the lavatories, and no reports of related injuries.

Sara Nelson, the international president of the Association of Flight Attendants-CWA, has a different perspective.

“The concerns are uniform across the industry,” said Nelson, who added that AFA-CWA does not represent Delta flight attendants, who are not unionized. Describing facing lavatories, she said that “the doors of these restrooms open into each other, creating safety issues. There are a lot of injuries, with smashed fingers, doors hitting people, bumps and bruises.”

Nelson said that the rear cabin restroom doors also create a barricade between the cabin and the back galley when open, limiting the ability of crew to maneuver if a passenger in the cabin is in trouble.

Some parents with small children say they cannot help their kids in the toilet unless the door stays open. Passengers of size, and those with physical challenges, say getting into the smaller lavatories is often not possible for them.

Jake Fitzpatrick, who is in the process of introducing a startup that reviews travel accommodations for the physically challenged, has cerebral palsy and uses a wheelchair, which requires a caregiver’s help to use the restroom.

When he takes Delta and Alaska Airlines, Fitzpatrick said it’s impossible for him to get into their single-aisle-aircraft bathrooms, so he uses restrooms at the airport before boarding.

“It’s hard to hold it, even for three to four hours,” said Fitzpatrick, who lives in Portland, Oregon. “If I go before, it takes 30 to 45 minutes to board everybody, and when we land, we often have to wait for a gate. A three- to four-hour flight means someone with a disability might have to wait five to six hours to go to the bathroom.”

Department of Transportation rules require at least one accessible lavatory on twin-aisle aircraft, but do not require accessible lavatories on single-aisle aircraft like the Boeing 373-900 or Airbus 320, which are used for many short- to medium-range flights.

Caitlin Harvey, a spokeswoman for the department, wrote in an email that the department has not received a significant number of written complaints from passengers with disabilities about the size of bathrooms on single-aisle aircraft.

However, she said, disability rights advocates have consistently raised the issue, advocating a rule requiring airlines to provide an accessible lavatory on single-aisle aircraft. So the department has formed the Advisory Committee on Accessible Air Transportation, which comprises industry representatives, disability rights advocates and other experts, to look into it.

“The committee is studying a range of promising design and layout solutions, both with respect to the lavatories themselves and with respect to onboard wheelchair design, that may be implemented in the short-term, medium-term and long-term,” Harvey wrote in an email. “The committee is also studying the costs and trade-offs that may come with imposing any new accessibility standards.”

Such changes can’t come soon enough for travelers like Wilma Abbey, a retired teacher from the Nashville area, whose two hip replacements have made maneuvering in airplane bathrooms very difficult.

“Just wait until someone gets stuck in one of those bathrooms, causing an emergency landing, and the airline gets sued,” Abbey said. “How much money do the airlines have to make before they provide the basic necessities? I’d like to see airline executives sit in coach and use the bathrooms they’ve provided us. It’s just an insult to the customers.”